5Upgrading an original Arcam Alpha

Back­ground

This old stal­wart dates back in design to about 1989 and I believe mine was made in 1991.  The Arcam Alpha uses one of the first DAC chips around, the fam­ous TDA1541(A).  Here’s a good page ded­ic­ated to play­ers fea­tur­ing this chip: Lamp­iz­at­or guy.  The author of that site is fam­ous in DIY circles but misses a few import­ant tricks when modi­fy­ing CD players.

Sec­tions to upgrade

I tend to think of CD play­ers as offer­ing three main areas for mak­ing sub­stan­tial sound qual­ity improve­ments: power sup­plies, clock­ing, out­put stage. Many novice upgraders nev­er pro­gress bey­ond fet­tling the ana­logue out­put sec­tion of a CD play­er.  This is a shame because the really big gains typ­ic­ally come from improv­ing power sup­plies and clock arrangements.

Power sup­plies

The Alpha is bet­ter than some as stand­ard, fea­tur­ing two power trans­formers and a 6 x 1000uF bank of smooth­ing caps for the DAC & op-amps.  It seems clear upon intern­al inspec­tion that Arcam have taken a gen­er­ic Philips PCB and power trans­former etc, then added their own DAC / out­put stage board which is powered by a second trans­former.  Sadly this trans­former is prone to mech­an­ic­al buzz­ing (a side effect of poorly con­struc­ted frame trans­formers).  One of my earli­er modi­fic­a­tions was to replace this with a tor­oid­al trans­former of the same sec­ond­ary voltages (17.5V — 0V — 17.5V).  The main PCB’s PSU caps power everything oth­er than the DAC chip and out­put op-amps.  Most, if not all, of these should be replaced, not only to improve sound qual­ity but also because the elec­tro­lyte in the caps could be dry­ing up after 20+ years!  It is fash­ion­able and indeed seems bene­fi­cial to change rec­ti­fier diodes with soft-recov­ery types, usu­ally “schot­tky”.  In my opin­ion this is a safe modi­fic­a­tion on digit­al sup­plies but may worsen the sound on ana­logue supplies.

To take things to a whole oth­er level it’s easi­est to mount some extra sup­plies off-board and run wires to it.  Remotely feed­ing my Alpha I have sup­plies for my new out­put stage, the digit­al fil­ter (SAA7220), decoder (SAA7310), servo driver chips as well as a trans­former ded­ic­ated to the after-mar­ket clock and the RAM IC.  The rec­ti­fic­a­tion and smooth­ing for clock sup­ply is on-board as I found on a pre­vi­ous pro­ject clock power sup­plies can cause issues when moun­ted externally.

For now I’ll just wrap this sec­tion up by say­ing use good qual­ity, LARGE capa­city caps on the DAC smooth­ing and you’ll be richly rewarded.

Clock­ing

For a long while it’s been a pop­u­lar modi­fic­a­tion to “re-clock” the DAC chip in your CD play­er.  Repla­cing the stand­ard tim­ing crys­tal with a low-jit­ter clock can be a subtle improve­ment or a pro­found one, depend­ing on the cir­cum­stances.  There are vari­ous after-mar­ket vendors of such clocks such as Tent Labs, Audi­ocom, LC and, more recently, Fidel­ity Audio.

Bey­ond DAC re-clock­ing, there are oppor­tun­it­ies to feed a “clean” clock sig­nal to oth­er parts of a CD play­er such as the decoder chip, digit­al fil­ter and maybe even parts of the servo.  In the Alpha I have so far fed 4 clock feeds from my Fidel­ity Audio C2 mas­ter clock.  Two of these re-clock pins on the DAC, one does the digit­al fil­ter and the oth­er the decoder.  Three of these are 11.2Mhz, the oth­er is 5.6Mhz (the main clock divided by two, which is avail­able on this par­tic­u­lar product).

If you go down this path you’ll be glad you did!

Out­put stage

The last thing I want to talk about is the out­put stage.  Arcam did a fair job on the power sup­plies, a typ­ic­ally poor job on the clock­ing and again let us down a little bit with the main out­put sec­tion, but there are far worse!  The out­put stage uses two single op-amps per chan­nel and some good qual­ity caps to fil­ter HF noise.  There’s noth­ing intrins­ic­ally wrong with op-amps but the ones avail­able at the time wer­en’t very good.  It’s pos­sible to upgrade these 4 op-amps and the res­ults would be good.  I tried to replace the final pair of op-amps with some Burr Brown OPA627, but I did­n’t get sound.  Without look­ing fur­ther into it I think it may be because they are not unity gain stable, mean­ing they can­not work purely as a “buf­fer”, they must amp­li­fy the signal.

The reas­on I looked no fur­ther was because I was build­ing up a whole new out­put stage using a PCB I sourced from the DIYAudio.com for­um.  This was designed by Nel­son Pass, a man fam­ous for his large class A amp­li­fi­er designs sold under the name Pass Labs.  This out­put stage was a quantum leap for­ward in son­ics!  Espe­cially so if, like me, you enjoy a warm full-bod­ied sound.  The power sup­ply for this is off-board.

Sum­mary

I will add to this art­icle as I think of improve­ments but it’s very dif­fi­cult to fit it all in as there is SO MUCH that can be done to an old CD play­er!  I would just hope to whet a few appet­ites of those seek­ing the elu­sive “per­fect sound forever” that Philips prom­ised us with the advent of the Com­pact Disc.  If you enjoyed this art­icle and want to request more detail on one par­tic­u­lar area then please drop in a com­ment, I’ll be sure to see it and respond.